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Wednesday 16th Apr 2014

Whether they’re gaffer tape crosses, flouro stickers or custom made – tracking markers are the most widely used item in any VFX supervisor’s kit bag. However in low light or on night shoots you’ll need illuminated tracking markers.

There’s established technique for producing tracking markers using heat shrink, a CR2302 battery and an LED (here’s a video tutorial for producing these markers).

The heatshrink style markers are really simple to produce and will work just fine. But they do have some limitations – they’re likely to spill lighting into the scene, they can’t be dimmed and finally as they don’t have a resister they’ll drain the battery quickly. Being able to reduce the intensity of the LED can help reduce the spill, but more importantly it can also reduce streaking effects on camera moves.

I thought I’d have a go at making some makers that are reusable (ie the battery can be easily replaced), can be dimmed and feature a resister to reduce the strain on the battery.

After a bit of experimenting I came up with this design and in this tutorial I’ll walk you through the parts required and the process to put them together.

LED Tracking Marker

Parts required

  1. 35mm Film tub
  2. Diffused white LED
  3. LED holder
  4. 33 or 48ohm resister (I used 48ohm)
  5. Variable resister / Trim pot
  6. Mini slide switch
  7. CR2302 Battery
  8. CR2302 Battery holder
  9. Stripboard

A couple of notes on the parts I selected – I chose diffused LED’s to reduce any unwanted flares that you could possibly get from a more intense light source, they also give a more consistent shape to track. For the switch it’s important to select the smallest possible otherwise the board won’t fit into the film canister (mine are 8mm long and 4mm wide). I bent the pins over to mount them on their side rather than buy the right angled versions.  You can buy the film canisters on eBay as well – in fact lets face it you can buy anything on eBay.

Equipment required

  1. Soldering Iron
  2. Small Screwdrivers
  3. Wire snips
  4. Hole widener (also known as a hand reamer)
  5. Hacksaw
  6. Desk clamp
  7. Hot glue gun
  8. Stripboard track cutter

I’ve built up a good selection of tools over the past couple of years and having just the right tool has become something of a (almost) middle age obsession. You don’t need much to put these markers together, however the hole widener and stripboard breaking tool really speed up the process. You can see the hole widening tool below, it has serrated metal blades and makes perfectly neat holes rather than tearing up the plastic canister with a knife.

Hole widening tool

The process

Firstly cut your stripboard down into 1 inch square sections. I applied masking tape to help prevent shattering. I also cut on the brass side as it makes separating the pieces much neater and prevents the brass strips from being torn off as you break them apart. Use a sharp knife to about half way through the stripboard and then you should be able to snap them apart.

CuttingStripBoard_02CuttingStripBoard_03

Next place all your components onto the stripboard. I’ve made a diagram below that will make an electronics engineer want to tear their eyes out, but hopefully it should help you place everything. Note that I mounted the battery holder on a very slight diagonal. Because of the protruding shape on the positive side of the holder this angle gives just a little more room to squash everything together into as small an area as possible so everything fits into the container.

LED stripboard layout

Once you’re happy with the layout hot glue the switch and the battery holder to the stripboard. This gives a little more strength when turning the marker on and off and when replacing the battery.

Use the stripboard track breaker to break the track between the two inputs of the trimmer pot (see the photograph below for reference). This means that current will only flow through one leg and out through the output. If you didn’t break the track here you’d have two positive inputs and the trimmer wouldn’t work correctly. Now you’re ready to solder the components onto the board. My soldering skills are appalling but the image below will give you an idea of what should go where.

Attaching components

Now it’s time to attach the cables and the LED. I cut two short cables and soldered them to the LED and then soldered them onto the stripboard, you’ll want to connect them as near to the other components as possible as we’re going to trim a lot of the excess stripboard away. You should also put the collar of the LED holder over the cables at this point so you don’t forget before you mount the LED into the holder.

This is a good point to test that everything works. You should be able to decrease the brightness of the LED by turning the trim pot.

Attach LED

Now compare your stripboard to the film canister. With some VERY careful snipping you should be able to trim off the edges and edge up with something that fits neatly inside.

Trimmed stripboards

Now it’s time to prepare the film canister. You want to trim it down so it’s about 22mm in height. Again I added masking tape so I could mark it up and try and avoid any damage, I placed the canister into a desk vice and used the hacksaw to cut it down.

Cutting film canister

Now using a pin or the end of a sharp file poke a hole in the top of the canister. Use the hole widener to carefully open up the hole for the LED holder.

Poking hole into film canister

Once you’ve got the hole the correct size, place the LED holder in and then push the LED through the other side. It’s a little fiddly to attach the collar but it’ll help hold the LED firmly in place. I added a little masking tape to prevent the cables from touching each other or the back of the stripboard, but some very thin heatshrink would have done a better job.

LED mounted

Now all that remains is to make a hole half way up the side of the canister for the power switch. Then push the stripboard in side, put the cap on and you’re done !

I added florescent orange stickers to the base of mine as to make it easier to find them in the dark. This has become a habit of mine having lost so many notepads, USB keys and what not in dark studios.

Finished tracking marker Finished tracking markers

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